This invention provides a method to substantially increase the accuracy and reduce the need for imaging related to placing an intravascular catheter or other device. Aspects of the invention relate to the guidance, positioning and placement confirmation of intravascular devices, such as catheters, stylets, guidewires and other elongate bodies that are typically inserted percutaneously into the venous or arterial vasculature, including flexible elongate bodies. Currently, these goals are suboptimally achieved using x-ray imaging, fluoroscopy, and in some cases ultrasound imaging. ECG alone is used but has severe limitations with accuracy, navigation along the entire venous pathway, and is of minimal value in the presence of arrhythmia or abnormal heart cardiac activity. Reduced imaging reduces the amount of radiation that patients are subjected to, reduces the time required for the procedure, and decreases the cost of the procedure by reducing the time needed in the radiology department. The degree of accuracy provided by the invention is critical because there are patient consequences to a catheter in a location that is not precisely correct.
The vasculature of mammals has long been accessed to provide therapy, administer pharmacological agents, and meet other clinical needs. Numerous procedures exist in both venous and arterial systems and are selected based on patient need. One challenge common to all vascular-based therapies is health care provider access to the specific location or section of the vascular tree.
One common venous access procedure is central venous access. Central venous access is the placement of a venous catheter in a vein that leads directly to the heart. Central venous catheters are ubiquitous in modern hospital and ambulatory medicine, with up to 8 million insertions per year in the U.S. and a similar number outside the U.S.
Venous access devices are most often used for the following purposes:                Administration of medications, such as antibiotics, chemotherapy drugs, and other IV drugs        Administration of fluids and nutritional compounds (hyperalimentation)        Transfusion of blood products        Hemodialysis        Multiple blood draws for diagnostic testing        
Consequences of cather tip placement inaccuracies include, among other things:                Increased risk of thrombis formation        Venous damage due to drug toxicity        Increased risk of infection        Additional radiation exposure        
Central venous access devices are typically small, flexible tubes placed in large veins for people who require frequent access to their bloodstream. The devices typically remain in place for long periods: week, months, or even longer.
Central venous access devices are usually inserted in one of three ways:                a) Directly. Catheters are inserted by tunneling under the skin into either the subclavian vein (located beneath the collarbone) or into the internal jugular vein (located in the neck). The part of the catheter where medications are administered or blood is drawn remains outside of the skin.        b) Through a port. Unlike catheters, which exit from the skin, ports are placed completely below the skin. With a port, a raised disk about the size of a quarter or half dollar is felt underneath the skin. Blood is drawn or medication delivered by placing a tiny needle through the overlying skin into the port or reservoir.        c) Indirectly via a periphal vein. Peripherally inserted central catheter (PICC) lines, unlike central catheters and ports, are not inserted directly into the central vein. A PICC line is inserted into a large vein in the arm and advanced forward into the larger subclavian vein.        
Central catheters and ports are usually inserted by a surgeon or surgical assistant in a surgical suite. A PICC line can be put in at bedside, usually by a specially-trained nurse. In this latter case, confirmation by X-ray is currently required for assessing the success of the PICC placement. Therefore PICC procedures as currently practiced involve exposure to X-ray, and manipulation of the catheter increases the risks of infection.
Traditional, surgically-placed central catheters are increasingly being replaced by peripherally inserted central venous access devices. PICC lines usually cause fewer severe complications than central venous access devices. The PICC line placement procedure is performed by interventional radiologists to deliver long-term drug delivery, chemotherapy procedures, delivery of intravenous medications or intravenous nutrition (hyperalimentation) and taking blood samples. Insertion of PICC lines is a routine procedure in that it is carried out for a variety of treatments, and more than once in the same patient when the catheter is to be left in place for any length of time. Even though it is routine, it is a very time and labor-intensive procedure for the hospital staff, which also makes it expensive. During the procedure the physician or nurse places the catheter into a superficial arm vein such as the cephalic, basilic, antecubital, median cubital, or other superficial vein with the goal of having the distal end of the catheter reach the superior vena cava. After entering the superficial vein around the area where the arm bends (elbow), the catheter is advanced up the subclavian vein, then the brachiocephalic vein and finally it enters the superior vena cava. One caveat is to make sure that the PICC line does not enter and remain in the jugular vein.
In addition to guiding the catheter through the vasculature, the final location of the catheter tip is very important to the success of the procedure. Catheters will generally function equally well for pressure measurement and fluid infusion if the tip is situated in any major vein, above the heart, or below the heart. For dialysis or the infusion of irritant/hypertonic fluids, a high rate of blood flow past the catheter tip is desirable and this requires the placement of the luminal opening in as large a vessel as possible. However, central venous catheter instructions for use give strong warnings about the requirement for catheter tips to lie outside the heart to avoid perforation and subsequent pericardial tamponade. Likewise positioning the catheter tip away from small peripheral veins is important to avoid damaging the vein wall or occluding the vein due the caustic effects of the infusing solution. An interventional radiologist may use a fluoroscopic agent to delineate the veins in the body and subsequently verify the correct positioning of the catheter tip using a post-operative X-ray. Currently, a post-operative X-ray is performed routinely while some studies have shown that only 1.5% of the cases are subject to complications that would indeed require X-ray imaging.
Current methods for guiding PICC lines include the legacy landmark measurement technique, X-ray guidance, external electromagnetic sensors, and intravascular sensors (e.g. ECG sensor). In the case of external electromagnetic sensors, the endovascular device is guided by assessing the distance between an electromagnetic element at the tip of the device (e.g. a coil) and an external (out of body) receiver. This method is inaccurate because it does not actually indicate location in the vascular but instead indicates only relative position to an external reference. In the case of ECG-guided catheters, the classic increase in P-wave size, known as “P-atriale”, is a widely accepted criterion for determining location of central venous catheter tips in the proximity of the sino-atrial node. Current methods include using a catheter filled with saline and an ECG adaptor at the proximal end connected to an ECG system. This method is inaccurate because it does not indicate location in the blood vessel but instead indicates the proximity of the sino-atrial node (SA node).
Because of known inaccuracies, all the current methods in use explicitly require the use of a confirmatory chest X-ray to verify and confirm location of the tip of the endovascular device at the desired target in the vasculature.
Additional approaches based on the use of non-imaging ultrasound are described in U.S. Patent Pub. Nos. 2007/0016068, 2007/0016069, 2007/0016070, and 2007/0016072, incorporated herein for all purposes. Limitations of an approach based exclusively on measuring right-atrial electrocardiograms have been described in the literature, for example, in [1]: W. Schummer et al., Central venous catheters—the inability of ‘intra-atrial ECCG’ to prove adequate positioning, British Journal of Anaesthesia, 93 (2): 193-8, 2004.
What is needed is a guidance system and method that overcome the above and other disadvantages of known systems and methods.
In view of the variable nature of physiological signal information used during endovascular positioning and guidance, what is needed are methods and apparatuses to optimize the use of physiological signal information and take into account the variable accuracy and usefulness of the signal information.
What is needed is a guidance system and method that can accurately position a device in irregular vascular environments such as the vasculature of patients with an aneurysm or arrhythmia.
What is needed is increased accuracy of the catheter tip placement without additional X-rays and manipulation of the catheter.